Foundation for Cordwood, dirt floor coop?

[NUHistorian]

Hi folks. I'm building a cordwood chicken coop, and I want it to have a dirt floor. I used a dirt floor/deep litter method with great success in Alaska, and want to do the same here in Vermont. I'm planning a 10 x 13 foot, rectangular, wood frame cordwood building like the Log End Sauna in Rob Roy's books.

Harvey Ussery suggests burying the foundation 18" deep to keep predators out. So I had a friend excavate an 18" deep rectangular trench. My plan was to build a foundation of three courses of concrete block, which would raise the foundation 6" above grade, at which point the frame and cordwood walls would begin.

Then the ADVICE started rolling in: It will frost heave. In Vermont foundations would have to be 4' deep, not 18" to avoid frost heaving.

I don't want to go deeper -- that would be a crazy big foundation. So what's the best approach? Stick with concrete blocks, which will be mostly buried to a depth of 18"? Or, my Plan B: bury hardware cloth or metal flashing to 18" around the outside to create a predator barrier, fill in the trenches, create a floating foundation on top with sand and either poured concrete or just one row of concrete block?

In Alaska I inherited a small stone building that worked just fine, so I never had to tackle the foundation/frost heaving problem. But I'm well aware of the effects of frost heaves, and I don't want to have my coop doors get stuck in the middle of winter.

 

[smhappe]

Have you considered using an earthbag foundation on a rubble trench? Rubble trenches are great for combating frost heave and for making sure moisture doesn't move into your walls. They are relatively simple and inexpensive to build (when compared to concrete foundations). Earthbags are a great option if you want to use available materials. If you couple an eathbag foundation with cordwood construction, you would end up with an unbeatable coop. Protection from predators, cool in the summer, warm in the winter, affordable, responsible, relatively simple for the DIYer and visually appealing.
Here is a website if you are interested in doing some further research:
http://www.earthbagbuilding.com/faqs/foundations.htm
http://www.earthbagbuilding.com/articles/diyeb.htm
I'd be interested to hear what you decide to do about your foundation and coop...especially if you do a hybrid earthbag/cordwood!
Good luck

 

[HickoryHollow]

NUHistorian
I am new to chickens, but have been doing construction for, like 300 years. lol. A lot of my experience comes from "alturnative" building types, such as cordwood, rough sawn, log, etc.

I love that you are doing cordwood construction. You WILL need some type of a footer though, or you will get sevier cracking. Your footer could be as simple as a gravel filled trench if the surounding soil has a lot of clay, or is rocky, or solid in some other way.

The footer needs to be at least as deep as the frost line in your area. It is 24 inches here in Ohio, but we usually go 30 to 36 inches deep with footers.

Wood frame structures can be made to "float" on skids on top of the ground, but if you involve mortar, such as brick, block, or cordwood construction, it will crack if it moves with the frost.

Hope this helps, and sorry to make you more work, but I wish you the best with your project!
Tim

 

[NUHistorian]

The earthbag foundation on a rubble trench sounds intriguing! But I think it may be way to much work for a 56-year-old woman with occasional student labor. On top of that, I live on a high ridge in Vermont with rocky "soil." Any fill for the bags (and the trench) will have to be trucked in. And I need to get this done before classes start in August so I'm under a time crunch.

But I'll definitely keep it in mind for the future. This coop is a kind of practice project so I can learn cordwood. If it goes well, I plan to build a much larger greenhouse/coop/rabbitry next year, on a circular plan. Perhaps I could try the earthbag foundation then.